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Six meta-analyses of the research literature on the only child were conducted in order to evaluate the status of the only child and to guide theory development in this area. The 117 studies included here generated enough information to justify six meta-analyses: Achievement Adjustment Character Intelligence Mental Illness and Sociability. Only children are found to surpass all others except firstborns and people from two-child families in Achievement and Intelligence. They also surpassed people from three- or more child families in Adjustment and Character. A model of the one-child family is developed that integrates the explanatory mechanisms of parental attention parental anxiety and family economic resources and emphasizes the strength of the parent-child relationship in small families. (EXCERPT)
Falbo et al. (Mon,) studied this question.